CSS4: Implement :placeholder-shown pseudo class

Source/core/css/resolver/SharedStyleFinder.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 77 matching lines @@
         if (willValidate && (candidate.isValidElement() != element().isValidElement()))
             return false;
 
         if (candidate.isInRange() != element().isInRange())
             return false;
 
         if (candidate.isOutOfRange() != element().isOutOfRange())
             return false;
     }
 
+    if (candidateInput.isPlaceholderVisible() != thisInput.isPlaceholderVisible())
+        return false;
+
     return true;
 }
 
 bool SharedStyleFinder::classNamesAffectedByRules(const SpaceSplitString& classNames) const
 {
     unsigned count = classNames.size();
     for (unsigned i = 0; i < count; ++i) {
         if (m_features.hasSelectorForClass(classNames[i]))
             return true;
     }
@@ skipping 239 matching lines @@
     // Tracking child index requires unique style for each node. This may get set by the sibling rule match above.
     if (!element().parentElementOrShadowRoot()->childrenSupportStyleSharing()) {
         INCREMENT_STYLE_STATS_COUNTER(*m_styleResolver, sharedStyleRejectedByParent, 1);
         return 0;
     }
 
     return shareElement->mutableComputedStyle();
 }
 
 }